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MgAlON ceramics with excellent optical properties were synthesized using high-purity AlON and commercially available MgO powder. The effect of MgO amount on ceramic sintering was examined in terms of microstructural evolution and grain growth. Furthermore, the process of MgAlON phase formation through the reaction between AlON and MgO was studied. The results revealed that the addition of MgO significantly hindered the formation of α-Al 2 O 3 and AlN phases at temperatures ranging from 1350 °C to 1600 °C, thereby facilitating the stabilization of the spinel-type phase. The optical transmittance and Vickers hardness of MgAlON were investigated through pressureless sintering followed by hot isostatic pressing (HIP). The resulting ceramics, with a MgO mass ratio of 10.0 wt%, exhibited an excellent in-line transmittance of ∼82.9 % at 0.6 μm and 87.7 % at 3.7 μm, and a remarkable Vickers hardness of approximately 13.65 ± 0.21 GPa. [ABSTRACT FROM AUTHOR]

In this study, fine Y2O3–MgO composite nanopowders were synthesized via the sol–gel method. Dense Y2O3–MgO composite ceramics were fabricated by pre‐sintering the green body in air at different temperatures for 1 h and then subjecting the sintered bodies to hot isostatic pressing at 1300°C for 1 h. The effects of pre‐sintering temperature on the microstructural, mechanical, and optical properties of the resulting ceramics were studied. The average grain size of the ceramics was increased, whereas their hardness and fracture toughness were decreased with increasing pre‐sintering temperature. A maximum fracture toughness of 1.42 MPa·m1/2 and Vickers hardness of 10.4 GPa were obtained. The average flexural strength of the ceramics was 411 MPa at room temperature and reached 361 MPa at 600°C. A transmittance of 84% in the 3–5 µm region was obtained when the composite ceramics were sintered at 1400°C. Moreover, a transmittance of 76% in the 3–5 µm region was obtained at 500°C. [ABSTRACT FROM AUTHOR]

In this study, highly transparent aluminate oxynitride (AlON) ceramics were prepared via the reactive sintering of Al2O3 and AlN powders using a Y2O3‐MgAl2O4‐H3BO3 ternary sintering additive. The ternary doping process resulted in the efficient preparation of transparent AlON ceramics with small grains and high transmittance as compared to the binary doping (Y2O3‐MgAl2O4) process. The addition of 0.1 wt.% Y2O3‐0.4 wt.% MgAl2O4‐0.12 wt.% H3BO3 resulted in the formation of a 4‐mm‐thick AlON ceramic with high transmittance (81% at 600 nm) and low haze (3.46%). This is the best performance in terms of the thickness and transmittance reported for AlON transparent ceramics prepared by the reactive sintering method. [ABSTRACT FROM AUTHOR]

Highly transparent Y2O3 ceramics using TiO2 as an additive were synthesized by presintering and hot isostatic pressing (HIP). The effects of TiO2 contents and sintering conditions on the optical properties of the final transparent ceramics were investigated. A small amount (0.04‐0.16 wt%) may decrease the densification temperature by about 200°C. The Y2O3 ceramics doped with 0.16 wt% TiO2 revealed a transparency of 82% in the wavelength range 1‐6 μm. The thermal conductivity of the samples is about 11.8 W/m K at 25°C, which is close to that of the undoped Y2O3 ceramics. [ABSTRACT FROM AUTHOR]

Despite being the most common sintering additive of transparent Y 2 O 3 ceramics, La 2 O 3 still suffers from weight changes when used in manufacturing processes due to its absorption of moisture and carbon dioxide. In the present work, two stable precursors, La(OH) 3 and La 2 O 2 CO 3 , were proposed for use as sintering additives for transparent Y 2 O 3 ceramics; La 2 O 3 powder was used for comparison. A series of experiments were conducted to investigate the influences of La 2 O 3 , La(OH) 3 and La 2 O 2 CO 3 on the optical properties of Y 2 O 3 ceramics by comparing the properties of mixed powders, green bodies and their sintering behaviors. Samples using La(OH) 3 or La 2 O 2 CO 3 as sintering additives exhibited more favorable optical properties at similar sintering temperatures compared to those using La 2 O 3 . Transmittances close to the theoretical value at 4 μm were achieved for samples doped with La(OH) 3 or La 2 O 2 CO 3 sintered at 1800 °C. [ABSTRACT FROM AUTHOR]

Crack is a common phenomenon in ceramics, which often extends and breaks the ceramic bodies. In the present study, however, cracks formed a network inside some transparent La-doped yttria ceramics, while didn’t break the samples. The reason was studied by investigating the mixed La 2 O 3 and Y 2 O 3 powders using SEM, TG-TDA BET, and XRD. The crack network is attributed to the volume effects of La(OH) 3 dehydration and solid state reaction of oxides, both proceed gradually instead of suddenly along with temperature increasing during heating procedure of sintering. Hence, the corresponding stresses made cracks inside La-doped yttria ceramics without broken the bodies. The cracks could be eliminated by increasing the powder calcination temperature to reduce the above volume effects. [ABSTRACT FROM AUTHOR]

Gd 2 O 3 –MgO composite ceramics are promising candidates for preparing protective mid-wave infrared (MWIR) windows. However, owing to the different crystal structures of Gd 2 O 3 and MgO after the sintering process, the volume ratio of the two phases must be controlled more precisely to achieve optimum performance. In this study, a nitrate-citrate combustion method was used to prepare Gd 2 O 3 –MgO nanopowders with different volume ratios, and composite ceramics were then fabricated via low-temperature pre-sintering and subsequent hot isostatic pressing (HIP). The effect of the Gd 2 O 3 :MgO volume ratio on the sintering behaviour, microstructures and optical, thermal and mechanical properties of the composite ceramics was studied in detail. A comprehensive assessment of the above-mentioned properties indicated that the Gd 2 O 3 –MgO composite ceramic with a volume ratio of 2:3, which exhibited a transmittance of 80.1–85.8% in the range of 3–5 μm, thermal conductivity of 17.5 W m−1 K−1, Vickers hardness of 9.8 GPa and toughness of 1.84 MPa m1/2, displays the optimum application performance for MWIR windows. [ABSTRACT FROM AUTHOR]

In this study, instrumented indentation experiments were performed under different loads on the polished surface of aluminum oxynitride (AlON) ceramics to investigate their surface fracture behavior and indentation response under quasi-static conditions. The results showed that the AlON transparent ceramics exhibited a typical indentation size effect (ISE) at the microloading scale, unlike the nano-indentation experiments, owing to a change in the material's destruction mechanism. The loading response process of the ceramics under the indenter shape was analyzed using different material parameters. The strain gradient effects were considered, and the ISE on the materials was characterized and analyzed. Based on the experimentally derived indentation stress-strain curve, an improved analytical model is proposed to estimate the stress field around an elastoplastic indentation/contact. The proposed model demonstrates excellent agreement with finite element analysis. The results suggest that a significant geometrical similarity exists in the conical indenter loading, and the state of the stress field is strongly dependent on the indentation index ε i. [ABSTRACT FROM AUTHOR]

Ceramic joining by glass is a promising method of the preparation of large transparent ceramics from small blocks. The chemical composition of glass was optimised to match the coefficient of thermal expansion and refractive index of transparent magnesium aluminate (MgAl 2 O 4) ceramics. A two-step joining method was developed to join MgAl 2 O 4 ceramics with a reduced number of bubbles in the joint, and the thermal properties of the optimised glass were evaluated to determine the joining temperature. Two transparent MgAl 2 O 4 blocks were joined by a glass layer that was approximately 20 µm thick. The joint area could not be distinguished with a naked eye. The transmittance of the joined body vertical to or parallel through the glass layer was approximately the same as that of the ceramics. The average three-point bending strength of the joint reached 202 ± 33 MPa, which was 64% that of the ceramic body. [ABSTRACT FROM AUTHOR]

Twin lamellas, were observed in transparent AlON ceramics in our previous work. In this work, the influence of the twin lamellas on mechanical strength was evaluated and its mechanism was investigated by SEM, EBSD, and HRTEM. Both the crystallographic direction and the space direction of a crack will deflect when it propagates across a twin lamella. The dynamic mechanism is that the dislocation propagation in front of the crack tips is blocked by the twin boundaries. Because the fraction of twin boundaries increases with grain size in transparent AlON ceramics, the strengthening effect becomes more notable for large-sized samples resulting in inverse Hall-Petch relation. It is a potentially useful way to advance the mechanical properties of transparent AlON ceramics by controlling the content of twin lamellas. [ABSTRACT FROM AUTHOR]

Highly transparent ZrO 2 -doped Y 2 O 3 ceramics were successfully synthesized using the hot isostatic pressing (HIP) process. The effects of the ZrO 2 content on the sintering behaviors, optical transmission spectra, Vickers hardness, grain size, size distribution, and Raman spectra were determined. The results indicated that decreased ZrO 2 content could promote increased transmittance, red-shifted infrared cutoff wavelength, increased thermal conductivity, decreased Vickers hardness, and increased lattice ordering. According to the optical transmission spectra, the optimized ZrO 2 content was 0.50 at%, at which point the ceramic exhibited a larger pre-sintering temperature range of 1650–1750 °C and the average grain size of 3.35 µm at 1750 °C. The grain size was significantly decreased at lower pre-sintering temperatures. Furthermore, a moderate Vickers hardness of 8.42 GPa and high thermal conductivity of 10.85 W/m K at room temperature were obtained for the optimized ceramic. [ABSTRACT FROM AUTHOR]

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd 2 O 3 and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd 2 O 3 is proved to have a lower lattice parameter (10.7516 Å) using XRD refinement. Pressureless sintering behavior of Gd 2 O 3 -MgO with/without 2 at% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400 °C while that of the undoped one shrinks sharply at 1250 °C due to Gd 2 O 3 phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd 2 O 3 creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3 %‐85.6 % at 3–5 µm, which show good consistency with the calculated values. The refractive index of Zr- Gd 2 O 3 varies from 1.87 at 3 µm to 1.80 at 5 µm, which is smaller than those of monoclinic Gd 2 O 3. [ABSTRACT FROM AUTHOR]

In this study, transparent AlON ceramics were fabricated via the direct ink writing (DIW) method from the water-based ceramic slurry. The solids loading of the ceramic slurry was optimised by changing the dispersant content, and the printability and water content were then adjusted by adding hydroxyethyl cellulose (HEC). The structure of the green body was complete and no impurity phases were detected. The effects of sintering temperature and dwell time on the bulk density, phase evolution, microstructure, in-line transmittance, and mechanical properties of the ceramics were studied systematically. High optical and mechanical properties of 10 × 10 × 0.9 mm3 single-phase AlON ceramic tiles were obtained by sintering at 1960 °C for 10 h in a nitrogen atmosphere: in-line transmittance of 81.90% at a wavelength of 780 nm, fracture toughness of 1.74 MPa·m1/2 (2.94 N), and Vickers hardness of 18.56 GPa (2.94 N). This study provides a novel method for synthesising AlON transparent ceramics from water-based ceramic slurries. [ABSTRACT FROM AUTHOR]

In this paper, highly transparent AlON ceramics were fabricated using hot isostatic pressing (HIP) assisted by dissolution of gas inclusions. The influence of additive content, pre-sintering, HIPing and annealing parameters on the sintered AlON ceramics were investigated and optimized. The obtained transparent AlON ceramics kept high transmittance 85.8 % and low loss coefficient 0.005 cm−1 at 2000 nm after annealing. Compared with different sintering additives and pre-sintering atmospheres, densification mechanism of the present material is revealed that SiO was formed from SiO 2 during pre-sintering under N 2 atmosphere occupying micropores which was then solidified and dissolved into AlON matrix in HIPing processing. This transformation and dissolution of gas into AlON ceramics make it possible to anneal the HIPed ceramics without degradation of microstructure and transmittance. [ABSTRACT FROM AUTHOR]

Alumina platelets were arranged horizontally in submicron alumina particles by shear force in the flow of slurries during casting. The obtained alumina green bodies with platelets were pressureless-sintered in vacuum, producing ceramics with thoroughly oriented grains and high transmittance. The effects of sintering parameters on the densification, microstructure evolution, and orientation degree of alumina ceramics were investigated and discussed. The results showed that the densification, grain size, orientation degree, and in-line transmittance were increased with increasing sintering temperature. The enhancement of orientation degree was mainly coherent with grain growth. The grain-oriented samples exhibited a much higher in-line transmittance (at 600 nm) of 61 % than that of the grain random sample (29 %). Moreover, the transmission remained a high level in the ultraviolet range (<300 nm). [ABSTRACT FROM AUTHOR]

Joining the transparent ceramic with metal could help to realise their applications. In this paper, the AlON ceramic was successfully bonded to the Ti6Al4V using the active element brazing approach. The microstructure of the achieved joints is characterised via scanning electron microscope (SEM), electron probe microanalyser (EPMA) and transmission electron microscope (TEM), which turned out to be AlON/Ti 3 (Cu,Al) 3 O/Ag(s,s) and Cu(s,s)/Ti 4 Cu/TiCu/Ti 2 Cu/Ti6Al4V. The effects of the brazing temperature and the holding time on the microstructure and the shear strength of the joint are investigated. It is found that with the increase of the brazing temperature and the holding time, the thickness of the Ti 3 (Cu, Al) 3 O, TiCu and Ti 2 Cu reaction layers increases while the thickness of the Ti 4 Cu reaction layer declines. The shear strength of the joint first increases with the brazing temperature/holding time and then decreases. The highest shear strength of 78.3 MPa is achieved when the joint is achieved at 840 °C for 10 min. The relationship between the joint microstructure and its mechanical properties is also revealed. [ABSTRACT FROM AUTHOR]

In this study, AlON powders with different AlN contents were synthesized by the carbothermal reduction nitridation method and used to prepare transparent AlON ceramics. Lattice parameters of AlON powders were calculated from XRD patterns to evaluate the effects on microstructure. The influences of the AlN content on the properties of the resulting AlON ceramics was investigated in aspect of density, mechanical properties and optical properties. With an increase in the AlN content, the density of the AlON ceramics increased, the grain size decreased, and the hardness and fracture toughness increased. Transparent AlON ceramics were obtained at the AlN content of 21.6–29.7 mol%. The refractive index of the AlON ceramics increased from 1.688 to 1.702 at 4000 nm with an increase of AlN content. The correlation between the composition and properties of the AlON ceramics obtained in this study will provide both theoretical and experimental reference for industrial AlON ceramic manufacturing. [ABSTRACT FROM AUTHOR]

An Nd 3+ -doped Sr 9 GdF 21 (SGF) transparent pore-free polycrystalline ceramic is produced by the ceramization of single crystals. The average transmittance (T A ) of the Nd 3+ -doped SGF ceramic (8-mm thick) is about 90.6% in the visible region and more than 92% in the near-IR region. The fracture toughness of the Nd 3+ -doped SGF ceramic is up to 1.28 MPa m 1/2 , which is significantly higher than that of similar types of ceramics. Gd 3+ ions, acting as both buffer ions and pinning ions, effectively improve the optical and mechanical properties of the SGF ceramic, implying that the sample is a promising candidate for high-power lasers. Moreover, the SGF ceramic shows a high mid- and far-infrared (up to 9 μm) transmittance, low phonon energy, and high density (ρ = 4.8466 g/cm 3 ), which pave the way for a wide range of applications such as infrared windows, mid- and far-infrared lasers, scintillators, and in photonics. [ABSTRACT FROM AUTHOR]

Transparent Nd-doped Ca 1 − x Y x F 2 + x ceramics were obtained through the ceramization of single crystals, and the morphology, microstructural characteristics, optical properties, and laser performance of the ceramics were examined. The results indicated that the microstructure of the transparent Nd-doped Ca 1 − x Y x F 2 + x ceramics was similar to that of traditional hot-pressed CaF 2 ceramics. In addition, the transparent Nd-doped Ca 1 − x Y x F 2 + x ceramics exhibited the same optical properties as the precursor single crystals. Furthermore, the ceramization of the precursor single crystals produced transparent Nd-doped Ca 1 − x Y x F 2 + x ceramics with mechanical properties (microhardness H = 3.430 GPa, fracture toughness K 1c = 0.61 MPa m 1/2 ) that were superior to that of the Nd-doped Ca 1 − x Y x F 2 + x single crystals. Continuous-wave laser operation with an output power of 35 mW was obtained through the application of a fiber-coupled laser diode with a central wavelength of approximately 808 nm. This suggests that the transparent Nd-doped Ca 1 − x Y x F 2 + x ceramics fabricated in this study are promising candidates for diode-pumped solid-state lasers and laser amplifiers. [ABSTRACT FROM AUTHOR]

Er3+ and Sm3+ ions were co-doped in Sr 2 SnO 4 : x Er3+/Sm3+ ceramics to achieve the integration of photo-stimulated luminescence (PSL), thermal-stimulated luminescence (TSL) and photochromism (PC) in one single material. The effect of doped Er3+ content on the microstructure, PC, PSL and TSL of the ceramcis has been investigated. It is found that moderate Er3+ content (x ≤ 0.003) could enhance PC, photoluminescence and TSL performance of the ceramics. The PSL and TSL are greatly depressed when x ≥ 0.005. This variation is caused by the change of kinds of formed defects. In addition, we have proposed a new method for optical information storage using the PSL as the optical signal, in which up-conversion luminescence from Er3+ is the reference signal. This strategy could prevent the occurring of error signal. A simple mechanism on the luminescence modulation, PC, PSL and TSL is proposed basing on the defect chemistry. The application demonstration shows the ceramics' potential in optical devices due to their multi-functional optical properties. • PC, PSL and TSL properties of Er3+/Sm3+ co-doped Sr 2 SnO 4 ceramic were investigated. • PSL occurs when 980 nm stimulated, with three peaks located at 582 nm, 622 nm and 672 nm. • The method using PSL signal can avoid the influence of original signal. • Moderate Er3+ concentration (x ≤ 0.003) could enhance PC, PL and TSL performance. • A new method for optical information storage based on PSL signal and UC signal has been proposed. [ABSTRACT FROM AUTHOR]